Objective lens for a microscope

ABSTRACT

Objective lens for a microscope of dry system high magnification having a leading lens element or group of which the lens element forming the air contacting surface at the image side is made of a glass having a high refractive index equal to or higher than 1.72 and a low index of dispersion equal to or higher than 50, the refracting surface at the object side of the lens element or group immediately succeeding the leading lens element or group being made convex toward the object while the amount of the airgap between the rearmost lens element or group and the lens element or group immediately preceding the rearmost than element or group is made equal to or greater than 0.7 times the focal length of the entire optical system of the objective lens, so that the various aberrations particularly the astigmatism and the curvature of field are widely compensated for.

emu-"91 SR [72] Invent Tofihllllmlufllke 3.355.234 11/1967 Muller .4350/176 ToltyDJlplll 3.437.398 4/l969 Mulleretal. 350/22OX 1970 PrimaryExaminer-John K. Corbin 4s Patented Nov.30. i971 [73] AssigneeOlympusOptlcalCm, Ltd.

TokyoJapan ABSTRACT: Objective lens for a microscope of dry system highmagnification having a leading lens element or group of which the lenselement forming the air contacting surface at [54] A MlCROSCOPE theimage side is made of a glass having a high refractive index 8 equal toor higher than l.72 and a low index of dispersion [52] U-S- Cl 35 /229,equal to or higher than 50. the refracting surface at the object 350/l75ML. 350/177 side of the lens element or group immediately succeeding the[51] Int. Cl G02b 9/12, leading lens element or group being made convextoward the G02b 21/02 object while the amount of the airgap between therearmost [50] FieldolSureh 350/229, lens element or group and the lenselement or group im- 22 I76. I77 mediately preceding the rearmost thanelement or group is made equal to or greater than 0.7 times the focallength of the [56] Reknnc Cmd entire optical system of the objectivelens. so that the various UNITED STATES PATENTS aberrations particularlythe astigmatism and the curvature of 2,78 l .694 2/1957 Takahashi350/229 field are Widely compensated Fl d Ld O

PATENTED unvaolsn 623,- 792 sum 1 or 4 Fig.

PRIOR ART INVENTOR rosmFvm may PATENTED M3019?! 3,623. 792

sum 2 or 4 [CURVATURE OF FIELD [DSTORTlON] ASTIGMATISM IN VENTORfosmfllm 0am:

PATENTEDNMOBII 3.623792 SHEET 3 OF 4 INVENTOR mam): venue PATENTEU uuvaoI97! SHEET 4 [IF 4 *5 O 5(mm)-2 O 2(/o) [CURVATURE OF FIELD [DISTORTON]ASTIGMATISM INVENTOR MRWI tic-TIME M N T OBJECTIVE LENS FOR A MICROSCOPEBACKGROUND OF THE INVENTION The present invention relates to anobjective lens for a microscope, and more particularly to a dry systemhigh magnification objective lens for a microscope.

The prior art objective lens of the type described above has sufferedits unavoidable undercorrection of astigmatism thereby resulting ininsufiicient resolution in the marginal zone of the field of view whilethe compensation of the curvature of field is insufficient in comparisonwith the proper Petzval image plane thereof due to the undercorrectionof the astigmatism thereby deteriorating the flatness of the imageplane, because the prior art objective lens has in general therefractive index and the index of dispersion of the lens element in theleading lens element or group forming the air-contacting surface at theimage side thereof less than 1.72 and 50, respectively, and therefracting surface at the object side of the lens element or groupimmediately succeeding the leading lens element or group is made concavetoward the object, while the airgap between the rearmost lens element orgroup and the lens element or group immediately preceding the rearmostlens element or group is relatively short, thereby making it difficultto compensate for the curvature of field and the spherical aberration aswell as axial chromatic aberration and the chromatic aberration ofmagnification while the compensating power for the astigmatism isentirely lost and the corrective power of the coma is made insufiicient.

The present invention aims to avoiding the disadvantages of the prior anobjective lens as described above.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a novel and useful objective lens for a microscope of the typedescribed above which positively eliminates the above-describeddisadvantages ofthe prior art objective lens.

Another object is to provide a novel and useful objective lens of thetype described above which has an improved fiatness of the image planewhile the resolution in the marginal zone of the field of view is widelyimproved.

The above objects are achieved in accordance with the present inventionby the provision of an objective lens charac terized by the fact thatthe lens element of the leading lens elementor group forming theaircontacting surface at the image side thereof is made of glassmaterial having a high refractive index and a low index of dispersionsatisfying the following requirements:

rid; 1.72

1111250 where nd and vd designate the refractive index and the index ofdispersion, respectively, and that the refracting surface at the objectside of the lens element or group immediately succeeding the leadinglens element or group is made convex toward the direction of the object,while the amount of the airgap between the rearmost lens element orgroup and the lens element or group immediately preceding the rearmostlens element or group is made relatively great so that the followingrequirement is satisfied:

0.7FD where F and D designate the focal length of the entire opticalsystem of the objective lens and the amount of the airgapbetween therearmost lens element or group and the preceding lens element or group.

In the present invention. the leading lens group located nearest to theobject may be made a single lens element, but it is essential to makethe lens element of the leading lens group forming the air-contactingsurface at the image side thereof by a glass material having thefollowing characteristics:

nd 1.72 M1250 where m1 and vd are the refractive index and the index ofdispersion, respectively. These requirements are referred to ascondition A hereinafter. The condition A is indispensable in order (1)to compensate for the curvature of field. (2) to remove the axialchromatic aberration as well as the chromatic aberration ofmagnification and (3) to compensate for the spherical aberration.

1f the above refractive index nd is made smaller than 1.72, then it ismade extremely difiicult to simultaneously remove the curvature of fieldand the spherical aberration. And, if the above index of dispersion ismade smaller than 50, then it is made almost impossible to compensatefor the axial chromatic aberration and the chromatic aberration ofmagnification simultaneously. Particularly, the chromatic aberration ofmagnification is extremely deteriorated.

Further, in the present invention, it is also essential to make therefracting surface at the object side of the lens element or groupimmediately succeeding the leading lens element or group convex towardthe object. This requirement is referred to as condition B hereinafter.The condition B makes it possible to sufficiently compensate for theserious undercorrection of the astigmatism unavoidably taking place inthe leading lens element or group.

If the above refractive surface is made concave toward the object, thenthe corrective power of the astigmatism is entirely lost. And, eventhough the above refracting surface is made flat, the correcting powerof the astigmatism is insufficient.

Finally, in the present invention, it is essential that the amount ofthe airgap between the rearmost lens element or group and the lenselement or group immediately preceding the rearmost lens element orgroup satisfies the following requirement:

where F and D designate the focal length of the entire optical system ofthe objective lens and the amount of the airgap between the rearmostlens element or group and the preceding lens element or group. Thisrequirement is referred to as condition C hereinafter. The condition Cis indispensable for compensating for the coma of the entire opticalsystem of the objective lens constructed in accordance with theconditions A and B.

If the above-described amount D of the airgap is made smaller than 0.7F,then the above-described correcting power of the coma is madeinsufficient.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview showing the construction of a dry system high magnificationobjective lens of the prior art;

FIGS. 2A-2C are diagrams showing various aberration curves of theobjective lens of FIG. 1;

FIG. 3 is a view similar to FIG. I but showing the preferred embodimentof the objective lens constructed in accordance with the presentinvention; and

FIGS. 4A-4C are similar to FIGS. 2A-2C but show various aberrationcurves of the objective lens shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1and 2A2C, the prior art objective lens is constructed of a leading lenselement, an intermediate lens group having two lens elements cemented toeach other and a rearmost lens group also comprised of two lens elementscemented to each other.

The numerical data of the objective lens of FIG. I are given in table 1below.

TABLE 1 'y d nd vd 1 0.641 1.523 60.0 2 x 3.8 1.0 3 3.85 0.26 1.740927.7 4 -40.0 0.56 1.0 5 8.01 1.90 1.7409 27.7 6 5.08 0.09 1.4886 69.8 718.9 0.56 1.0

The symbols 7, d designate the radius of curvature of the lens elementsincluding cover glass and the thickness of the lens elements or theairgap between the adjacent two lens elements including cover glass,while nd, vd designate the refractive index and the index of dispersionof the lens elements including cover glass.

FIGS. ZA-ZC show the various aberration curves of the objective lensshown in table 1.

As seen from FIG. 2B, the astigmatism is undercorrected so that theresolution of the marginal zone of the field of of view is notsatisfactory. Also, the compensation for the curvature of field isinsufficient due to the undercorrection of the astigmatism.

The objective lens of the present invention shown in FIG. 3 has thenumerical data shown in table 2 and the various aberration curves of theobjective lens of table 2 are shown in F IGS. 4A-4C.

TABLE 2 'y d nd l d 1 0.669 1.523 60.0 2 --24.1 1.7 L 3 9.Z L9 L699 30.04 0.25 1.789 51.0 5 +l2.4 0.67 1.0 6 +5.32 1.70 1.785 26.0 7 7.02 4.301.486 82.0 X +107 0.99 1.0 9 +5.85 L99 1.717 48.0 10 l2.5 1.488 70.0

[.0 Thickness ul'Cover Glass S,=0. l 7 Magnification B=40.0X

Numerical Aperture N.A. =0.65

The symbols y and d designate the radius of curvature of lens elementsincluding cover glass and the thickness of the lens elements or theamount of the airgap between the adjacent two lens elements includingcover glass, respectively, and nd and W1 designate the refractive indexand the index of dispersion of the lens elements including cover glass,respectively, while the numerals at the leftmost column designate theorder of the arrangement of the lens elements including cover glassbeginning at the side of the leading lens element.

As is evident from the comparison of FIGS. 4A-4C and FIG. 2A2C, thevarious aberrations such as the spherical aberration, the axialchromatic aberration, the coma OSC, the chromatic aberration ofmagnification. the astigmatism, the curvature of field, and thedistortion of the present invention are highly compensated for incomparison with the prior art objective lens, particularly, theimprovement in the compensation for the astigmatism and the curvature offield is remarkable.

Iclaim:

1. Objective lens for a microscope comprised of a leading lenscomponent, a lens component immediately succeeding said leading lenscomponent with an airgap provided therebetween and a rearmost lenscomponent with an airgap provided between the same and a lens componentimmediately preceding said rearmost lens component, wherein theimprovement comprises the fact that the air-contacting surface of saidleading lens component at the image side thereof is formed by a lenselement of said leading lens component which is made of a glass materialhaving a high refractive index and a low index of dispersion satisfyingthe following requirements:

M1250 where nd and vd designate the refractive index and the index ofdispersion, respectively, the refracting surface at the object side ofsaid lens com%onent immediately succeeding said leadmg lens componentemg made convex toward the d|rect|on of the object, the amount D of theairgap between said rearmost lens component and said lens componentimmediately preceding said rearmost lens component satisfying thefollowing requirement:

where F designates the focal length of the entire optical system ofsaidobjective lens, said lens having the following numerical data:

7 d nd ml 1 1 0.669 1.523 60.0 2 -24.1 1.7 1.0 3 9.25 L9 L699 300 43.S-8 0.25 1.789 51.0 5 +114 0.67 1.0 6 +5.32 1.70 1.785 26.0 7 7.024.30 1.486 82.0

[.0 Thickness of Cover Glass S,=0. l 7 Magnification B=-4(l,0X

Numerical Aperture N.A. =0.

where y and d designate the radius of curvature of the lens elementsincluding cover glass and the thickness of the lens elements or theamount of the airgap between the adjacent two lens elements includingcover glass, respectively, and mi and u d designate the refractive indexand the index of dispersion of the lens elements includingcover glass,respectively, while the numerals at the leftmost column designate theorder of the arrangement of the lens elements including cover glassbeginning at the side ofthe leading lens element.

1. Objective lens for a microscope comprised of a leading lenscomponent, a lens component immediately succeeding said leading lenscomponent with an airgap provided therebetween and a rearmost lenscomponent with an airgap provided between the same and a lens componentimmediately preceding said rearmost lens component, wherein theimprovement comprises the fact that the air-contacting surface of saidleading lens component at the image side thereof is formed by a lenselement of said leading lens component which is made of a glass materialhaving a high refractive index and a low index of dispersion satisfyingthe following requirements: nd 1.72 Nu d 50 where nd and Nu d designatethe refractive index and the index of dispersion, respectively, therefracting surface at the object side of said lens component immediatelysucceeding said leading lens component being made convex toward thedirection of the object, the amount D of the airgap between saidrearmost lens component and said lens component immediately precedingsaid rearmost lens component satisfying the following requirement: 0.7FD where F designates the focal length of the entire optical system ofsaid objective lens, said lens having the following numerical data:gamma d nd Nu d 1 infinity 0.669 1.523 60.0 2 - 24.1 1.7 1.0 3 - 9.251.9 1.699 30.0 4 3.54 0.25 1.789 51.0 5 + 12.4 0.67 1.0 6 + 5.32 1.701.785 26.0 7 - 7.02 4.30 1.486 82.0 8 + 20.7 0.99 1.0 9 + 5.85 1.991.717 48.0 10 - 12.5 1.488 70.0 1.0 Thickness of Cover Glass S1 -0.17Magnification B -40.0X Numerical Aperture N.A. 0.65 where gamma and ddesignate the radius of curvature of the lens elements including coverglass and the thickness of the lens elements or the amount of the airgapbetween the adjacent two lens elements including cover glass,respectively, and nd and Nu d designate the refractive index and theindex of dispersion of the lens elements including cover glass,respectively, while the numerals at the leftmost column designate theorder of the arrangement of the lens elements including cover glassbeginning at the side of the leading lens element.